High-strength sputtering target for forming protective film for optical recording medium

ABSTRACT

A high-strength sputtering target for forming a protective film for an optical recording medium, obtained by sintering a mixed powder containing, in mol %, 10 to 70% of a zirconium oxide or hafnium oxide and 50% or less (over 0%) of silicon dioxide, and 0.1 to 8.4% of yttrium oxide as necessary, and the remainder containing aluminum oxide, lanthanum oxide, or indium oxide and inevitable impurities, wherein a complex oxide phase of Al 6 Si 2 O 13 , La 2 SiO 5 , or In 2 Si 2 O 7  is formed in a base of the target.

FIELD OF THE INVENTION

The present invention relates to a high-strength sputtering target (hereinafter, referred to as “target”) for forming a protective film for an optical recording medium which is capable of recording, reading out, repeatedly recording and reading out, and erasing information using a laser beam.

Priority is claimed on Japanese Patent Application No. 2006-159303, filed Jun. 8, 2006, the content of which is incorporated herein by reference.

BACKGROUND OF THE INVENTION

It is generally known that protective films (hereinafter including both lower and upper protective films) for an optical recording medium such as a laser disk or the like typically include 20% of silicon dioxide (SiO₂) with the remaining part being zinc sulfide (ZnS). This protective film is known to be obtained by carrying out sputtering with the use of a target for forming a protective film for an optical recording medium, i.e., a ZnS—SiO₂ based hot-press sinter which includes 20% silicon dioxide (SiO₂) with the remaining part being zinc oxide (ZnS).

However, such a protective film prepared by using a target composed of a ZnS—SiO₂ based hot-press sinter causes a problem in that repeatable re-recording performance deteriorates when a laser beam is irradiated to a recording layer to repetitively perform re-recording since S in ZnS of a target composed of a ZnS—SiO₂ based hot-press sinter diffuses in the recording layer. Consequently, development of a protective film containing no S has been carried out. Examples of a protective film containing no S, as follows, are known where values are in mol %.

(i) A protective film for an optical recording medium produced by sintering a mixed powder including 10 to 70% of zirconium oxide, and 50% or less (over 0%) of silicon dioxide, and the remainder containing aluminum oxide and inevitable impurities.

(ii) A protective film for an optical recording medium produced by sintering a mixed powder including 10 to 70% of hafnium oxide, 50% or less (over 0%) of silicon dioxide and the remainder containing aluminum oxide and inevitable impurities.

(iii) A protective film for an optical recording medium produced by sintering a mixed powder including 10 to 70% of zirconium oxide, 0.1 to 8.4% of yttrium oxide, and 50% or less (over 0%) of silicon dioxide, and the remainder containing aluminum oxide and inevitable impurities.

(iv) A protective film for an optical recording medium produced by sintering a mixed powder including 10 to 70% of zirconium oxide, and 50% or less (over 0%) of silicon dioxide, and the remainder containing lanthanum oxide and inevitable impurities.

(v) A protective film for an optical recording medium produced by sintering a mixed powder including 10 to 70% of hafnium oxide, and 50% or less (over 0%) of silicon dioxide, and the remainder containing lanthanum oxide and inevitable impurities.

(vi) A protective film for an optical recording medium produced by sintering a mixed powder including 10 to 70% of zirconium oxide, 0.1 to 8.4% of yttrium oxide, and 50% or less (over 0%) of silicon dioxide, and the remainder containing lanthanum oxide and inevitable impurities.

(vii) A protective film for an optical recording medium produced by sintering a mixed powder including 10 to 70% of zirconium oxide, and 50% or less (over 0%) of silicon dioxide, and the remainder containing indium oxide and inevitable impurities.

(viii) A protective film for an optical recording medium produced by sintering a mixed powder including 10 to 70% of hafnium oxide, and 50% or less (over 0%) of silicon dioxide, and the remainder containing indium oxide and inevitable impurities.

(ix) A protective film for an optical recording medium produced by sintering a mixed powder including 10 to 70% of zirconium oxide, 0.1 to 8.4% of yttrium oxide, and 50% or less (over 0%) of silicon dioxide, and the remainder containing indium oxide and inevitable impurities.

In addition, a target for forming protective films for an optical recording medium which have compositions described in the foregoing (i) to (ix) has been developed. This target has the same composition as the protective films for an optical recording medium mentioned in (i) to (ix) above (refer to Japanese Patent Application Laid-Open No. 2005-56545).

The target employs the oxide powders mentioned in the foregoing (i) to (ix) as a raw powder. The raw powders are mixed at a predetermined ratio and combined to prepare a mixed powder. The mixed powders are molded and baked in air or an oxidative atmosphere such as an oxygen atmosphere, thereby producing the targets.

SUMMARY OF THE INVENTION

In targets produced by mixing oxide powders prepared as in (i) to (ix) as raw powders at a predetermined ratio and combining into mixed powders, followed by molding and baking the mixed powders in an oxidative atmosphere under normal conditions, cracks occur during high-power sputtering, and thus formation of a protective group for an optical recording medium cannot be efficiently achieved.

An object of the present invention is to provide a high-strength target for forming a protective film for an optical recording medium in which cracks do not occur even in high-power sputtering.

The inventors of the present invention have carried out extensive studies to produce a high-strength target for forming a protective film for an optical recording medium without producing cracks even in high-power sputtering. As a result, the following results are obtained.

(a) As for a sputtering target for forming a protective film for an optical recording medium produced by sintering a mixed powder including 10 to 70% of zirconium oxide, and 50% or less (over 0%) of silicon dioxide, and the remainder containing aluminum oxide and inevitable impurities; a sputtering target for forming a protective film for an optical recording medium produced by sintering a mixed powder including 10 to 70% of hafnium oxide, and 50% or less (over 0%) of silicon dioxide, and the remainder containing aluminum oxide and inevitable impurities; or a sputtering target for forming a protective film for an optical recording medium produced by sintering a mixed powder containing 10 to 70% of zirconium oxide, 0.1 to 8.4% of yttrium oxide, and 50% or less (over 0%) of silicon dioxide, and the remainder containing an aluminum oxide and inevitable impurities; a target having a structure in which a complex oxide phase of Al₆Si₂O₁₃ is formed in a target base has further improved density and strength. Thus, cracks do not occur in the target during high-power sputtering.

(b) As for a sputtering target for forming a protective film for an optical recording medium produced by sintering a mixed powder including 10 to 70% of zirconium oxide, and 50% or less (over 0%) of silicon dioxide, and the remainder containing lanthanum oxide and inevitable impurities; a sputtering target for forming a protective film for an optical recording medium produced by sintering a mixed powder including 10 to 70% of hafnium oxide, and 50% or less (over 0%) of a silicon dioxide, and the remainder containing a lanthanum oxide and inevitable impurities; or a sputtering target for forming a protective film for an optical recording medium produced by sintering a mixed powder including 10 to 70% of zirconium oxide, 0.1 to 8.4% of yttrium oxide, and 50% or less (over 0%) of silicon dioxide, and the remainder containing a lanthanum oxide and inevitable impurities; a target having a structure in which a complex oxide phase of La₂SiO₅ is formed in a target base has further improved density and strength. Thus, cracks do not occur in the target during high-power sputtering.

(c) As for a sputtering target for forming a protective film for an optical recording medium produced by sintering a mixed powder including 10 to 70% of zirconium oxide, and 50% or less (over 0%) of silicon dioxide, and the remainder containing indium oxide and inevitable impurities; a sputtering target for forming a protective film for an optical recording medium produced by sintering a mixed powder including 10 to 70% of hafnium oxide, and 50% or less (over 0%) of silicon dioxide, and the remainder containing an indium oxide and inevitable impurities; or a sputtering target for forming a protective film for an optical recording medium produced by sintering a mixed powder including 10 to 70% of zirconium oxide, 0.1 to 8.4% of yttrium oxide, and 50% or less (over 0%) of silicon dioxide, and the remainder containing an indium oxide and inevitable impurities; a target having a structure in which a complex oxide phase of In₂Si₂O₇ is formed in a target base has further improved density and strength. Thus, cracks do not occur in the target during high-power sputtering. A target having a structure in which a complex oxide phase of In₂Si₂O₇ is formed in a target base gives more remarkably improved density and strength as compared to a target having no complex oxide phase of In₂Si₂O₇.

The present invention has been made on the basis of these study results.

(1) According to a first embodiment of the invention, there is provided a high-strength sputtering target for forming a protective film for an optical recording medium, obtained by sintering a mixed powder including, in mol %, 10 to 70% of zirconium oxide, and 50% or less (over 0%) of silicon dioxide, and the remainder containing an aluminum oxide and inevitable impurities; the target has a structure in which a complex oxide phase of Al₆Si₂O₁₃ is formed in a target base. More preferably, the content of the zirconium oxide is in the range of 20 to 50 mol %, and the content of the silicon dioxide is in the range of 10 to 30 mol %.

(2) According to another embodiment of the invention, there is provided a high-strength sputtering target for forming a protective film for an optical recording medium, obtained by sintering a mixed powder including, in mol %, 10 to 70% of hafnium oxide, and 50% or less (over 0%) of silicon dioxide, and the remainder containing aluminum oxide and inevitable impurities; the target has a structure in which a complex oxide phase of Al₆Si₂O₁₃ is formed in a target base. More preferably, the content of the hafnium oxide is in the range of 20 to 50 mol %, and the content of the silicon oxide is in the range of 10 to 30 mol %.

(3) According to another embodiment of the present invention, there is provided a high-strength sputtering target for forming a protective film for an optical recording medium, obtained by sintering a mixed powder including, in mol %, 10 to 70% of zirconium oxide, 0.1 to 8.4% of yttrium oxide, and 50% or less (over 0%) of a silicon dioxide, and the remainder containing an aluminum oxide and inevitable impurities; the target has a structure in which a complex oxide phase of Al₆Si₂O₁₃ is formed in a target base. More preferably, the content of the zirconium oxide is in the range of 20 to 50 mol %, and the content of the silicon oxide is in the range of 10 to 30 mol %.

(4) According to another embodiment of the present invention, there is provided a high-strength sputtering target for forming a protective film for an optical recording medium, obtained by sintering a mixed powder including, in mol %, 10 to 70% of zirconium oxide, and 50% or less (over 0%) of silicon dioxide, and the remainder containing lanthanum oxide and inevitable impurities; the target has a structure in which a complex oxide phase of La₂SiO₅ is formed in a target base. More preferably, the content of the zirconium oxide is in the range of 20 to 50 mol %, and the content of the silicon oxide is in the range of 10 to 30 mol %.

(5) According to another embodiment of the present invention, there is provided a high-strength sputtering target for forming a protective film for an optical recording medium, obtained by sintering a mixed powder including, in mol %, 10 to 70% of hafnium oxide, and 50% or less (over 0%) of silicon dioxide, and the remainder containing lanthanum oxide and inevitable impurities; the target has a structure in which a complex oxide phase of La₂SiO₅ is formed in a target base. More preferably, the content of the hafnium oxide is in the range of 20 to 50 mol %, and the content of the silicon oxide is in the range of 10 to 30 mol %.

(6) According to another embodiment of the present invention, there is provided a high-strength sputtering target for forming a protective film for an optical recording medium, obtained by sintering a mixed powder including, in mol %, 10 to 70% of zirconium oxide, 0.1 to 8.4% of yttrium oxide, and 50% or less (over 0%) of silicon dioxide, and the remainder containing lanthanum oxide and inevitable impurities, the target has a structure in which a complex oxide phase of La₂SiO₅ is formed in a target base. More preferably, the content of the zirconium oxide is in the range of 20 to 50 mol %, and the content of the silicon oxide is in the range of 10 to 30 mol %.

(7) According to another embodiment of the present invention, there is provided a high-strength sputtering target for forming a protective film for an optical recording medium, obtained by sintering a mixed powder including, in mol %, 10 to 70% of zirconium oxide, and 50% or less (over 0%) of silicon dioxide, and the remainder containing indium oxide and inevitable impurities; the target has a structure in which a complex oxide phase of In₂Si₂O₇ is formed in a target base. More preferably, the content of the zirconium oxide is in the range of 20 to 50 mol %, and the content of the silicon oxide is in the range of 10 to 30 mol %.

(8) According to another embodiment of the present invention, there is provided a high-strength sputtering target for forming a protective film for an optical recording medium, obtained by sintering a mixed powder including, in mol %, 10 to 70% of hafnium oxide, and 50% or less (over 0%) of silicon dioxide, and the remainder containing indium oxide and inevitable impurities; the target has a structure in which a complex oxide phase of In₂Si₂O₇ is formed in a target base. More preferably, the content of the hafnium oxide is in the range of 20 to 50 mol %, and the content of the silicon oxide is in the range of 10 to 30 mol %.

(9) According to another embodiment of the present invention, there is provided a high-strength sputtering target for forming a protective film for an optical recording medium, obtained by sintering a mixed powder including, in mol %, 10 to 70% of zirconium oxide, 0.1 to 8.4% of yttrium oxide, and 50% or less (over 0%) of silicon dioxide, and the remainder containing indium oxide and inevitable impurities; the target has a structure in which a complex oxide phase of In₂Si₂O₇ is formed in a target base. More preferably, the content of the zirconium oxide is in the range of 20 to 50 mol %, and the content of the silicon oxide is in the range of 10 to 30 mol %.

For producing a high-strength sputtering target for forming a protective film for an optical recording medium according to the present invention, zirconium oxide powder, yttira stabilized zirconia powder, hafnium oxide powder, amorphous silicon dioxide powder, aluminum oxide powder, lanthanum oxide powder, and indium oxide powder are employed as raw powders. These raw powders are combined and mixed to give compositions mentioned in (1) to (9), thereby preparing mixed powders. The mixed powders are press molded, after which the molded bodies are actively sintered at 1300° C. or higher, which is higher than the usual sintering temperature, in an oxygen atmosphere, thereby producing targets.

When producing a high-strength sputtering target for forming a protective film for an optical recording medium according to the present invention, it is crucial to use an amorphous silicon dioxide powder as the raw powder, to adopt an oxygen atmosphere, and to conduct baking at a temperature of 1300° C. or higher. If a crystalline silicon dioxide power is used, warpage occurs in the produced target, which is not preferable as the strength decreases. Furthermore, zirconium oxide powder to be used as the raw powder may be a stabilized or partially-stabilized zirconium oxide powder. As such the stabilized or partially-stabilized zirconium oxide powder, for example, there is a zirconium oxide powder containing 1 to 12 mol % of Y₂O₃.

A target for forming a protective film of an optical recording medium according to the invention can be made larger since the strength of the protective film is further improved. Moreover, since cracks do not form in the target even under a high-power sputtering, a protective film for an optical recording medium can be formed more efficiently.

BEST MODE FOR CARRYING OUT THE INVENTION

Hereinbelow, the target for forming a protective film for an optical recording medium according to the present invention will be described in more detail with reference to Examples.

The following powders were prepared as the raw powders: ZrO₂ powder having an average particle diameter of 0.2 μm and a purity of 99.99% or higher, HfO₂ powder having an average particle diameter of 0.2 μm and a purity of 99.99% or higher, SiO₂ powder having an average particle diameter of 0.2 μm and a purity of 99.99% or higher, SiO₂ powder having an average particle diameter of 1 μm and a purity of 99.99% or higher, In₂O₃ powder having an average particle diameter of 0.5 μm and a purity of 99.99% or higher, Al₂O₃ powder having an average particle diameter of 0.5 μm and a purity of 99.99% or higher, and La₂O₃ powder having an average particle diameter of 0.5 μm and a purity of 99.99% or higher. In addition, a stabilized ZrO₂ powder containing 3 mol % of Y₂O₃ was also prepared.

Example 1

The ZrO₂ powder, amorphous SiO₂ powder, crystalline SiO₂ powder, and Al₂O₃ powder were weighed to give the composition shown in Table 1 and uniformly mixed by a Henschel mixer. Subsequently, the mixed powder was press-molded, after which the obtained molded body was baked under the conditions given in Table 1, thereby producing an inventive target 1 and a conventional target 1, both of which had a diameter of 200 mm and a thickness of 6 mm and included 30% of ZrO₂, and 20% of SiO₂, and the remainders containing Al₂O₃. The cross sections of the target 1 of the present invention and the conventional target 1 were polished and observed through X-ray diffraction and an EPMA to determine whether or not a complex oxide phase of Al₆Si₂O₁₃ was formed in the bases of the targets. The results of which are given in Table 1. Furthermore, the density and flexural strength of the target 1 of the present invention and the conventional target 1 were measured. The results are shown in Table 1.

Then, the produced target 1 of the present invention and the produced conventional target 1 were mounted in a direct current magnetron sputtering system, in a state of being soldered with a water-cooled backing plate made of oxygen-free copper. First, the inside of the system was evacuated to be 1×10⁻⁶ Torr or less using a vacuum air exhauster. Then, an Ar gas was introduced into the system so as to give a pressure of sputtering gas of 1.5×10⁻³ Torr. A polycarbonate substrate with a thickness of 0.6 mm was disposed at an interval of 70 mm, i.e., the interval of the targets. In this state, a direct current power, i.e., a sputtering power of 9 kW which was higher than the norm, was applied, and protective films for an optical recording medium, having a thickness of 50 nm, were formed on a surface of the polycarbonate substrate, using the target 1 of the present invention and the conventional target 1, respectively. Here, observation to determine whether or not cracks are formed in the targets was made. The results of which are shown in Table 1.

TABLE 1 Existence or Properties of Target Nonexistence Existence or Conditions of Baking of Complex Nonexistence Composition of Raw Powder (mol %) Tem- Keeping Oxide of Flexural of Cracks Amorphous Crystalline perature Time Al₆Si₂O₁₃ in Density Strength during Target ZrO₂ SiO₂ SiO₂ Al₂O₃ Atmosphere (° C.) (h) Target Base (%) (MPa) Sputtering Present 1 30 20 — remainder oxygen 1400 7 Existent 96 275 Nonexistent Invention Conventional 1 30 — 20 remainder air 1200 7 Nonexistent 85 150 Existent Invention

The results given in Table 1 show that the target 1 of the present invention in which the complex oxide phase of Al₆Si₂O₁₃ was formed in the base has a higher density and strength and does not give cracks upon sputtering as compared to the conventional target 1 in which the complex oxide phase of Al₆Si₂O₁₃ was not formed in the base, even if both had the same composition.

Example 2

The HfO₂ powder, amorphous SiO₂ powder, crystalline SiO₂ powder, and Al₂O₃ powder were weighed to give the composition shown in Table 2 and uniformly mixed by a Henschel mixer. Subsequently, the mixed powder was press-molded, after which the obtained molded body was baked under the conditions given in Table 2, thereby producing an inventive target 2 and a conventional target 2, both of which had a diameter of 200 mm and a thickness of 6 mm and included 30% of HfO₂, and 20% of SiO₂, and the remainders containing Al₂O₃. The cross sections of the target 2 of the present invention and the conventional target 2 were polished and observed through X-ray diffraction and an electron probe micro analyzer (EPMA) to determine whether or not a complex oxide phase of Al₆Si₂O₁₃ was formed in the bases of the targets, the results of which are given in Table 2. Furthermore, the density and flexural strength of the target 2 of the present invention and the conventional target 2 were measured. The results are shown in Table 2.

Then, the produced target 2 of the present invention and the produced conventional target 2 were mounted in a direct current magnetron sputtering system, in a state of being soldered with a water-cooled backing plate made of oxygen-free copper. First, the inside of the system was evacuated to be 1×10⁻⁶ Torr or less using a vacuum air exhauster. Then, an Ar gas was introduced into the system so as to give a pressure of sputtering gas of 1.5×10⁻³ Torr. A polycarbonate substrate with a thickness of 0.6 mm was disposed at an interval of 70 mm, i.e., the interval of the targets. In this state, direct current power, i.e., a sputtering power of 7 kW which was higher than norm, was applied, and protective films for an optical recording medium, having a thickness of 50 nm, were formed on a surface of the polycarbonate substrate, using the target 2 of the invention and the conventional target 2, respectively. Here, observation to determine whether or not cracks are formed in the targets was made. The results of which are shown in Table 2.

TABLE 2 Existence or Properties of Target Nonexistence Existence or Conditions of Baking of Complex Nonexistence Composition of Raw Powder (mol %) Tem- Keeping Oxide of Flexural of Cracks Amorphous Crystalline perature Time Al₆Si₂O₁₃ in Density Strength during Target HfO₂ SiO₂ SiO₂ Al₂O₃ Atmosphere (° C.) (h) Target Base (%) (MPa) Sputtering Present 2 30 20 — Remainder oxygen 1400 7 Existent 97 220 Nonexistent Invention Conventional 2 30 — 20 Remainder air 1200 7 Nonexistent 85 145 Existent Invention

The results given in Table 2 show that the target 2 of the present invention in which the complex oxide phase of Al₆Si₂O₁₃ was formed in the base has a higher density and strength and does not give cracks upon sputtering as compared to the conventional target 2 in which the complex oxide phase of Al₆Si₂O₁₃ was not formed in the base, even if both had the same composition.

Example 3

The stabilizer ZrO₂ powder containing 3 mol % of Y₂O₃, amorphous SiO₂ powder, crystalline SiO₂ powder, and Al₂O₃ powder were weighed to give the composition given in Table 3 and uniformly mixed by a Henschel mixer. Subsequently, the mixed powder was press-molded, after which the obtained molded body was baked under the conditions given in Table 3, thereby producing a target 3 of the present invention and a conventional target 3, both of which had a diameter of 200 mm and a thickness of 6 mm and included 30% of ZrO₂, and 0.9% of Y₂O₃, 20% of SiO₂, and the remainders containing Al₂O₃. The cross sections of the target 3 of the present invention and the conventional target 3 were polished and observed through X-ray diffraction and an electron probe micro analyzer (EPMA) to determine whether or not a complex oxide phase of Al₆Si₂O₁₃ was formed in the bases of the targets, the results of which are given in Table 3. Furthermore, the density and flexural strength of the target 3 of the present invention and the conventional target 3 were measured. The results are shown in Table 3.

Then, the produced target 3 of the present invention and the produced conventional target 3 were mounted in a direct current magnetron sputtering system, in a state of being soldered with a water-cooled backing plate made of oxygen-free copper. First, the inside of the system was evacuated to be 1×10⁻⁶ Torr or less using a vacuum air exhauster. Then, an Ar gas was introduced into the system so as to give a pressure of sputtering gas of 1.5×10⁻³ Torr. A polycarbonate substrate with a thickness of 0.6 mm was disposed at an interval of 70 mm, i.e., the interval of the targets. In this state, a direct current power, i.e., a sputtering power of 9 kW which was higher than the norm, was applied, and protective films for an optical recording medium, having a thickness of 50 nm, were formed on the polycarbonate substrate, using the target 3 of the present invention and the conventional target 3, respectively. Here, observation to determine whether or not cracks are formed in the targets was made. The results of which are shown in Table 3.

TABLE 3 Composition of Raw Powder (mol %) Existence or Properties of Target Stabilizer Conditions of Baking Nonexistence Existence or ZrO₂ Tem- of Complex Nonexistence Containing pera- Keeping Oxide of Flexural of Cracks 3 mol % of Amorphous Crystalline Atmos- ture Time Al₆Si₂O₁₃ in Density Strength during Target Y₂O₃ SiO₂ SiO₂ Al₂O₃ phere (° C.) (h) Target Base (%) (MPa) Sputtering Present 3 30 20 — Remainder oxygen 1400 7 Existent 99 280 Nonexistent Invention Conventional 3 30 — 20 Remainder air 1200 7 Nonexistent 92 200 Existent Invention

The results given in Table 3 show that the target 3 of the present invention in which the complex oxide phase of Al₆Si₂O₁₃ was formed in the base has a higher density and strength and does not give upon sputtering as compared to the conventional target 3 in which the complex oxide phase of Al₆Si₂O₁₃ was not formed in the base, even if both had the same composition.

Example 4

The ZrO₂ powder, amorphous SiO₂ powder, crystalline SiO₂ powder, and La₂O₃ powder were weighed to give the composition given in Table 4 and uniformly mixed by a Henschel mixer. Subsequently, the mixed powder was press-molded, after which the obtained molded body was baked under the conditions given in Table 4, thereby producing a target 4 of the present invention and a conventional target 4, both of which had a diameter of 200 mm and a thickness of 6 mm and included 30% of ZrO₂, and 20% of SiO₂, and remainders containing La₂O₃. The cross sections of the target 4 of the present invention and the conventional target 4 were polished and observed through X-ray diffraction and an electron probe micro analyzer (EPMA) to determine whether or not a complex oxide phase of La₂SiO₅ was formed in the bases of the targets. The results of which are given in Table 4. Furthermore, the density and flexural strength of the target 4 of the present invention and the conventional target 4 were measured. The results are shown in Table 4.

Then, the produced target 4 of the present invention and the produced conventional target 4 were mounted in a direct current magnetron sputtering system, in a state of being soldered with a water-cooled backing plate made of oxygen-free copper. First, the inside of the system was evacuated to be 1×10⁻⁶ Torr or less using a vacuum air exhauster. Then, an Ar gas was introduced into the system so as to give a pressure of sputtering gas of 1.5×10⁻³ Torr. A polycarbonate substrate with a thickness of 0.6 mm was disposed at an interval of 70 mm, i.e., the interval of the targets. In this state, a direct current power, i.e., a sputtering power of 9 kW which was higher than the norm, was applied, and protective films for an optical recording medium, having a thickness of 50 nm, were formed on a surface of the polycarbonate substrate, using the target 4 of the present invention and the conventional target 4, respectively. Here, observation to determine whether or not cracks are formed in the targets was made. The results of which are shown in Table 4.

TABLE 4 Existence or Properties of Target Conditions of Baking Nonexistence Existence or Tem- of Complex Nonexistence Composition of Raw Powder (mol %) pera- Oxide of Flexural of Cracks Amorphous Crystalline ture Keeping La₃SiO₅ in Density Strength during Target ZrO₂ SiO₂ SiO₂ La₂O₃ Atmosphere (° C.) Time (h) Target Base (%) (MPa) Sputtering Present 4 30 20 — Remainder oxygen 1400 7 Existent 95 190 Nonexistent Invention Conventional 4 30 — 20 Remainder air 1200 7 Nonexistent 85 110 Existent Invention

The results given in Table 4 show that the target 4 of the present invention in which the complex oxide phase of La₂SiO₅ was formed in the base has a higher density and strength and does not give cracks upon sputtering as compared to the conventional target 4 in which the complex oxide phase of La₂SiO₅ was not formed in the base, even if both had the same composition.

Example 5

The HfO₂ powder, amorphous SiO₂ powder, crystalline SiO₂ powder, and La₂O₃ powder were weighed to give the composition given in Table 5 and uniformly mixed by a Henschel mixer. Subsequently, the mixed powder was press-molded, after which the obtained molded body was baked under the conditions given in Table 5, thereby producing a target 5 of the present invention and a conventional target 5, both of which had a diameter of 200 mm and a thickness of 6 mm and included 30% of HfO₂, and 20% of SiO₂, and the remainders containing La₂O₃. The cross sections of the target 5 of the present invention and the conventional target 5 were polished and observed through X-ray diffraction and an electron probe micro analyzer (EPMA) to determine whether or not a complex oxide phase of La₂SiO₅ was formed in the bases of the targets. The results of which are given in Table 5. Furthermore, the density and flexural strength of the target 5 of the present invention and the conventional target 5 were measured. The results of which are shown in Table 5.

Then, the produced target 5 of the present invention and the produced conventional target 5 were mounted in a direct current magnetron sputtering system, in a state of being soldered with a water-cooled backing plate made of oxygen-free copper. First, the inside of the system was evacuated to be 1×10⁻⁶ Torr or less using a vacuum air exhauster. Then, an Ar gas was introduced into the system so as to give a pressure of sputtering gas of 1.5×10⁻³ Torr. A polycarbonate substrate with a thickness of 0.6 mm was disposed at an interval of 70 mm, i.e., the interval of the targets. In this state, a direct current power, i.e., a sputtering power of 7 kW which was higher than the norm, was applied, and protective films for an optical recording medium, having a thickness of 50 nm, were formed on a surface of the polycarbonate substrate, using the target 5 of the present invention and the conventional target 5, respectively. Here, observation to determine whether or not cracks are formed in the targets was made. The results of which are shown in Table 5.

TABLE 5 Existence or Properties of Target Conditions of Baking Nonexistence Existence or Tem- of Complex Nonexistence Composition of Raw Powder (mol %) pera- Oxide of Flexural of Cracks Amorphous Crystalline ture Keeping La₃SiO₅ in Density Strength during Target HfO₂ SiO₂ SiO₂ La₂O₃ Atmosphere (° C.) Time (h) Target Base (%) (MPa) Sputtering Present 5 30 20 — Remainder oxygen 1400 7 Existent 98 180 Nonexistent Invention Conventional 5 30 — 20 Remainder air 1200 7 Nonexistent 85 100 Existent Invention

The results given in Table 5 show that the target 5 of the present invention in which the complex oxide phase of La₂SiO₅ was formed in the base has a higher density and strength and does not give cracks upon sputtering as compared to the conventional target 5 in which the complex oxide phase of La₂SiO₅ was not formed in the base, even if both had the same composition.

Example 6

The stabilizer ZrO₂ powder containing 3 mol % of Y₂O₃, amorphous SiO₂ powder, crystalline SiO₂ powder, and La₂O₃ powder were weighed to give the composition shown in Table 6 and uniformly mixed by a Henschel mixer. Subsequently, the mixed powder was press-molded, after which the obtained molded body was baked under the condition given in Table 6, thereby producing a target 6 of the present invention and a conventional target 6, both of which had a diameter of 200 mm and a thickness of 6 mm and included 30% of ZrO₂, and 0.9% of Y₂O₃, 20% of SiO₂ and the remainders containing La₂O₃. The cross sections of the target 6 of the present invention and the conventional target 6 were polished and observed through X-ray diffraction and an electron probe micro analyzer (EPMA) to determine whether or not a complex oxide phase of La₂SiO₅ was formed in the bases of the targets. The results of which are given in Table 6. Furthermore, the density and flexural strength of the target 6 of the present invention and the conventional target 6 were measured. The results are shown in Table 6.

Then, the produced target 6 of the present invention and the produced conventional target 6 were mounted in a direct current magnetron sputtering system, in a state of being soldered with a water-cooled backing plate made of oxygen-free copper. First, the inside of the system was evacuated to be 1×10⁻⁶ Torr or less using a vacuum air exhauster. Then, an Ar gas was introduced into the system so as to give a pressure of sputtering gas of 1.5×10⁻³ Torr. A polycarbonate substrate with a thickness of 0.6 mm was disposed at an interval of 70 mm, i.e., the interval of the targets. In this state, a direct current power, i.e., a sputtering power of 9 kW which was higher than the norm, was applied, and protective films for an optical recording medium, having a thickness of 50 nm, were formed on a surface of the polycarbonate substrate, using the target 6 of the present invention and the conventional target 6, respectively. Here, observation to determine whether or not cracks are formed in the targets was made. The results of which are shown in Table 6.

TABLE 6 Existence or Composition of Raw Powder (mol %) Nonexistence Properties of Target Stabilizer Conditions of Baking of Complex Existence or ZrO₂ Tem- Oxide of Nonexistence Containing pera- Keeping La₃SiO₅ Flexural of 3 mol Amorphous Crystalline Atmos- ture Time in Target Density Strength Cracks during Target % of Y₂O₃, SiO₂ SiO₂ La₂O₃ phere (° C.) (h) Base (%) (MPa) Sputtering Present 6 30 20 — Remainder oxygen 1400 7 Existent 96 220 Nonexistent Invention Conventional 6 30 — 20 Remainder air 1200 7 Nonexistent 89 145 Existent Invention

The results given in Table 6 show that the target 6 of the present invention in which the complex oxide phase of La₂SiO₅ was formed in the base has a higher density and strength and does not give cracks upon sputtering as compared to the conventional target 6 in which the complex oxide phase of La₂SiO₅ was not formed in the base, even if both had the same composition.

Example 7

The ZrO₂ powder, amorphous SiO₂ powder, crystalline SiO₂ powder, and In₂O₃ powder were weighed to give the composition shown in Table 7 and uniformly mixed by a Henschel mixer. Subsequently, the mixed powder was press-molded, after which the obtained molded body was baked under the condition given in Table 7, thereby producing a target 7 of the present invention and a conventional target 7, both of which had a diameter of 200 mm and a thickness of 6 mm and included 30% of ZrO₂, and 20% of SiO₂, and the remainders containing In₂O₃. The cross sections of the target 7 of the present invention and the conventional target 7 were polished and observed through X-ray diffraction and an electron probe micro analyzer (EPMA) to determine whether or not a complex oxide phase of In₂Si₂O₇ was formed in the bases of the targets. The results of which are given in Table 7. Furthermore, the density and flexural strength of the target 7 of the present invention and the conventional target 7 were measured. The results of which are shown in Table 7.

Then, the produced target 7 of the present invention and the produced conventional target 7 were mounted in a direct current magnetron sputtering system, in a state of being soldered with a water-cooled backing plate made of oxygen-free copper. First, the inside of the system was evacuated to be 1×10⁻⁶ Torr or less using a vacuum air exhauster. Then, an Ar gas was introduced into the system so as to give a pressure of sputtering gas of 1.5×10⁻³ Torr. A polycarbonate substrate with a thickness of 0.6 mm was disposed at an interval of 70 mm, i.e., the interval of the targets. In this state, a direct current power, i.e., a sputtering power of 9 kW which was higher than the norm, was applied, and protective films for an optical recording medium, having a thickness of 50 nm, were formed on a surface of the polycarbonate substrate, using the target 7 of the present invention and the conventional target 7, respectively. Here, observation to determine whether or not cracks are formed in the targets was made. The results of which are shown in Table 7.

TABLE 7 Properties of Target Conditions of Baking Existence or Existence or Tem- Nonexistence of Nonexistence Composition of Raw Powder (mol %) pera- Keeping Complex Oxide Flexural of Cracks Amorphous Crystalline ture Time of In₂Si₂O₇ in Density Strength during Target ZrO₂ SiO₂ SiO₂ In₂O₃ Atmosphere (° C.) (h) Target Base (%) (MPa) Sputtering Present 7 30 20 — Remainder oxygen 1400 7 Existent 99 255 Nonexistent Invention Conventional 7 30 — 20 Remainder air 1200 7 Nonexistent 90 150 Existent Invention

The results given in Table 7 show that the target 7 of the present invention in which the complex oxide phase of In₂Si₂O₇ was formed in the base has a higher density and strength and does not give cracks upon sputtering as compared to the conventional target 7 in which the complex oxide phase of In₂Si₂O₇ was not formed in the base, even if both had the same composition.

Example 8

The HfO₂ powder, amorphous SiO₂ powder, crystalline SiO₂ powder, and In₂O₃ powder were weighed to give the composition shown in Table 8 and uniformly mixed by a Henschel mixer. Subsequently, the mixed powder was press-molded, after which the obtained molded body was baked under the conditions given in Table 8, thereby producing a target 8 of the present invention and a conventional target 8, both of which had a diameter of 200 mm and a thickness of 6 mm and included 30% of HfO₂, and 20% of SiO₂, and the remainders containing In₂O₃. The cross sections of the target 8 of the present invention and the conventional target 8 were polished and observed through X-ray diffraction and an electron probe micro analyzer (EPMA) to determine whether or not a complex oxide phase of In₂Si₂O₇ was formed in the bases of the target. The results of which are given in Table 8. Furthermore, the density and flexural strength of the target 8 of the present invention and the conventional target 8 were measured. The results are shown in Table 8.

Then, the produced target 8 of the present invention and the produced conventional target 8 were mounted in a direct current magnetron sputtering system, in a state of being soldered with a water-cooled backing plate made of oxygen-free copper. First, the inside of the system was evacuated to be 1×10⁻⁶ Torr or less using a vacuum air exhauster. Then, an Ar gas was introduced into the system so as to give a pressure of sputtering gas of 1.5×10⁻³ Torr. A polycarbonate substrate with a thickness of 0.6 mm was disposed at an interval of 70 mm, i.e., the interval of the targets. In this state, a direct current power, i.e., a sputtering power of 7 kW which was higher than the norm, was applied, and protective films for an optical recording medium, having a thickness of 50 nm, were formed on a surface of the polycarbonate substrate, using the target 8 of the present invention and the conventional target 8, respectively. Here, observation to determine whether or not cracks are formed in the targets was made. The results of which are shown in Table 8.

TABLE 8 Existence or Properties of Target Conditions of Baking Nonexistence Existence or Tem- of Complex Nonexistence Composition of Raw Powder (mol %) pera- Oxide of Flexural of Cracks Amorphous Crystalline ture Keeping In₂Si₂O₇ in Density Strength during Target HfO₂ SiO₂ SiO₂ In₂O₃ Atmosphere (° C.) Time (h) Target Base (%) (MPa) Sputtering Present 8 30 20 — Remainder oxygen 1400 7 Existent 98 200 Nonexistent Invention Conventional 8 30 — 20 Remainder air 1200 7 Nonexistent 90 150 Existent Invention

The results given in Table 8 show that the target 8 of the present invention in which the complex oxide phase of In₂Si₂O₇ was formed in the base has a higher density and strength and does not give cracks upon sputtering as compared to the conventional target 8 in which the complex oxide phase of In₂Si₂O₇ was not formed in the base, even if both had the same composition.

Example 9

The stabilizer ZrO₂ powder containing 3 mol % of Y₂O₃, amorphous SiO₂ powder, crystalline SiO₂ powder, and In₂O₃ powder were weighed to give the composition shown in Table 9 and uniformly mixed by a Henschel mixer. Subsequently, the mixed powder was press-molded, after which the obtained molded body was baked under the condition given in Table 9, thereby producing a target 9 of the present invention and a conventional target 9, both of which had a diameter of 200 mm and a thickness of 6 mm and included 30% of ZrO₂, 0.9% of Y₂O₃, and 20% of SiO₂ and the remainders containing In₂O₃. The cross sections of the target 9 of the present invention and the conventional target 9 were polished and observed through X-ray diffraction and an electron probe micro analyzer (EPMA) to determine whether or not a complex oxide phase of In₂Si₂O₇ was formed in the bases of the targets. The results of which are given in Table 9. Furthermore, the density and flexural strength of the target 9 of the present invention and the conventional target 9 were measured. The results are shown in Table 9.

Then, the produced target 9 of the present invention and the produced conventional target 9 were mounted in a direct current magnetron sputtering system, in a state of being soldered with a water-cooled backing plate made of oxygen-free copper. First, the inside of the system was evacuated to be 1×10⁻⁶ Torr or less using a vacuum air exhauster. Then, an Ar gas was introduced into the system so as to give a pressure of sputtering gas of 1.5×10⁻³ Torr. A polycarbonate substrate with a thickness of 0.6 mm was disposed at an interval of 70 mm, i.e., the interval of the targets. In this state, a direct current power, i.e., a sputtering power of 9 kW which was higher than the norm, was applied, and protective films for an optical recording medium, having a thickness of 50 nm, were formed on a surface of the polycarbonate substrate, using the target 9 of the present invention and the conventional target 9, respectively. Here, observation to determine whether or not cracks are formed in the targets was made. The results of which are shown in Table 9.

TABLE 9 Existence or Composition of Raw Powder (mol %) Nonexistence Properties of Target Stabilizer Conditions of Baking of Existence or ZrO₂ Tem- Complex Oxide Nonexistence Containing pera- Keeping of In₂Si₂O₇ Flexural of 3 mol Amorphous Crystalline Atmos- ture Time in Target Density Strength Cracks upon Target % of Y₂O₃, SiO₂ SiO₂ In₂O₃ phere (° C.) (h) Base (%) (MPa) Sputtering Present 9 30 20 — Remainder oxygen 1400 7 Existent 99 255 Nonexistent Invention Conventional 9 30 — 20 Remainder air 1200 7 Nonexistent 90 150 Existent Invention

The results given in Table 9 show that the target 9 of the present invention in which the complex oxide phase of In₂Si₂O₇ was formed in the base has a higher density and strength and does not give cracks upon sputtering as compared to the conventional target 9 in which the complex oxide phase of In₂Si₂O₇ was not formed in the base, even if both had the same composition.

As described above, a target for forming a protective film for an optical recording medium according to the present invention can be formed in a large size due to even more improved strength. Moreover, as cracks do not form in the target even under high-power sputtering, a protective film for an optical recording medium can be formed more efficiently. Accordingly, the present invention is substantially useful for industrial applications. 

1. A high-strength sputtering target for forming a protective film for an optical recording medium, obtained by sintering a mixed powder comprising, in mol %, 10 to 70% of zirconium oxide, 50% or less (over 0%) of silicon dioxide, and the remainder containing aluminum oxide and inevitable impurities, wherein a complex oxide phase of Al₆Si₂O₁₃ is formed in a base of the target.
 2. A high-strength sputtering target for forming a protective film for an optical recording medium, obtained by sintering a mixed powder comprising, in mol %, 10 to 70% of hafnium oxide, and 50% or less (over 0%) of silicon dioxide, and the remainder containing aluminum oxide and inevitable impurities, wherein a complex oxide phase of Al₆Si₂O₁₃ is formed in a base of the target.
 3. A high-strength sputtering target for forming a protective film for an optical recording medium, obtained by sintering a mixed powder comprising, in mol %, 10 to 70% of zirconium oxide, 0.1 to 8.4% of yttrium oxide, and 50% or less (over 0%) of silicon dioxide, and the remainder containing aluminum oxide and inevitable impurities, wherein a complex oxide phase of Al₆Si₂O₁₃ is formed in a base of the target.
 4. A high-strength sputtering target for forming a protective film for an optical recording medium, obtained by sintering a mixed powder comprising, in mol %, 10 to 70% of zirconium oxide, and 50% or less (over 0%) of silicon dioxide, and the remainder containing lanthanum oxide and inevitable impurities, wherein a complex oxide phase of La₂SiO₅ is formed in a base of the target.
 5. A high-strength sputtering target for forming a protective film for an optical recording medium, obtained by sintering a mixed powder comprising, in mol %, 10 to 70% of hafnium oxide, and 50% or less (over 0%) of silicon dioxide, and the remainder containing lanthanum oxide and inevitable impurities, wherein a complex oxide phase of La₂SiO₅ is formed in a base of the target.
 6. A high-strength sputtering target for forming a protective film for an optical recording medium, obtained by sintering a mixed powder comprising, in mol %, 10 to 70% of zirconium oxide, 0.1 to 8.4% of yttrium oxide, and 50% or less (over 0%) of silicon dioxide, and the remainder containing lanthanum oxide and inevitable impurities, wherein a complex oxide phase of La₂SiO₅ is formed in a base of the target.
 7. A high-strength sputtering target for forming a protective film for an optical recording medium, obtained by sintering a mixed powder comprising, in mol %, 10 to 70% of zirconium oxide, and 50% or less (over 0%) of silicon dioxide, and the remainder containing indium oxide and inevitable impurities, wherein a complex oxide phase of In₂Si₂O₇ is formed in a base of the target.
 8. A high-strength sputtering target for forming a protective film for an optical recording medium, obtained by sintering a mixed powder comprising, in mol %, 10 to 70% of hafnium oxide, and 50% or less (over 0%) of silicon dioxide, and the remainder containing indium oxide and inevitable impurities, wherein a complex oxide phase of In₂Si₂O₇ is formed in a base of the target.
 9. A high-strength sputtering target for forming a protective film for an optical recording medium, obtained by sintering a mixed powder comprising, in mol %, 10 to 70% of zirconium oxide, 0.1 to 8.4% of yttrium oxide, and 50% or less (over 0%) of silicon dioxide, and the remainder containing indium oxide and inevitable impurities, wherein a complex oxide phase of In₂Si₂O₇ is formed in a base of the target. 